Andy Flower knows who will accompany Andrew Strauss to the crease here on Friday when England meet Bangladesh. But he is not going to tell us.

There are three possibilities, now that Kevin Pietersen is heading home because his hernia is too painful for him to continue playing in this World Cup. Strauss's opening partner will be Ian Bell, Ravi Bopara or Matt Prior. "It does not have to be the same man for the rest of the tournament," said Flower. "You need different qualities to open the batting against Bangladesh than you do against Australia. We are going to have to be flexible."

Flower expressed disappointment at Pietersen's departure. "He is a world-class player and he was complementing Strauss in a very interesting way. We thought they would pose problems in this World Cup." This pair had posted three 50-partnerships in the tournament, even though Pietersen had squandered three good starts and had yet to produce the major innings.

Pietersen is to be replaced by Eoin Morgan, who is scheduled to arrive in Chittagong on Tuesday. "He [Morgan] will be straight into the nets. He is a skilful, no-nonsense cricketer. I can envisage him playing straight away," said Flower. Morgan was in the original World Cup party but was forced to withdraw with a broken finger. That finger has healed more quickly than expected with the anticipated operation not being necessary. Flower, making the best of an unwelcome situation, added: "Both he and we are lucky. Hopefully he will play an important part in this World Cup."

Flower just about hid his frustration at Pietersen's sudden departure. On Saturday the ECB disclosed Pietersen's hernia and the intention to manage the injury for the rest of the tournament. Forty-eight hours later, after a rousing victory against South Africa, Pietersen is on his way home. "He has had this problem for weeks and the clear medical advice was that he was not going to damage himself by playing on," explained Flower. "We hoped he would get through the tournament OK, take painkillers when needed and bite the bullet.

"But after the South Africa game his feeling is that it is too sore to keep playing international cricket. I empathise with anyone with a serious injury. In that situation you have just got to listen to what the injured player says.

"The timing is not ideal. But after a period of rehab he should be fine for the Test series [against Sri Lanka, which begins on 26 May]. But I would think that the IPL comes too soon for him [Pietersen has a contract with the Deccan Chargers]."

Pietersen's bowling will also be missed. He delivered eight respectable overs against South Africa on a turning track without any obvious signs of discomfort. More pitches like the one in Chennai and he would have bowled a number of overs in the remaining games of the tournament. However, despite a lean spell for England in ODIs it is Pietersen the batsman who will be most missed. He still has the capacity to threaten any attack.

All three of the contenders to replace him as an opening batsman have done the job before but it is self-evident that none of them have made a very good fist of it. If they had they would already be in place at the top of the order.

If Flower is serious about a truly flexible arrangement Prior might be trusted against Bangladesh's attack, which lacks pace. Then he may prefer a technically superior batsman — such as Bell — if England come up against Australia's fast bowlers later in the tournament.

In the meantime we have an intriguing little guessing game to play during the long days in Chittagong before Friday. At least – on the basis that you are only as good as your last game – England await that match against Bangladesh with some equanimity. After defeating South Africa they know that a victory on Friday means that qualification is secure.

Flower seemed happier talking about Sunday's game against South Africa than Pietersen's departure. "I find these low-scoring games more interesting than when 330 runs are scored. Our guys did brilliantly to fight back from 15 for three. [Jonathan] Trott and Bopara resurrected the innings with great maturity and Strauss was excellent tactically."

Neither Flower nor his men out on the field lost heart even when South Africa were coasting at 63-0 in pursuit of 171. "One of the traits of a good side is that they don't know how to give up," said Flower.

After that victory the impression is that, while they will miss Pietersen's potential for runs and possibly his overs, the England squad still feel there are possibilities without him in this World Cup, – especially on surfaces that give the bowlers a chance.